Battery packs including a plurality of batteries accommodated in a case to allow an output of a predetermined voltage and capacitance are widely used as power sources of various devices, vehicles, etc. Specifically, the technique of forming modules of battery assemblies obtained by connecting general-purpose batteries in parallel and/or in series to output a predetermined voltage and capacitance, and combining the battery modules together to be applicable to various applications is beginning to be used. This module forming technique can reduce the size and weight of the battery modules themselves by increasing the performance of batteries accommodated in the battery modules. Thus, this module forming technique has various advantages, an example of which is that workability can be improved in assembling a battery pack, and the flexibility in mounting the battery module in areas of limited space, such as a vehicle, can be increased.
Generally, a battery module includes a plurality of batteries accommodated in a battery case, wherein wires electrically connecting electrodes of the batteries to each other in series or in parallel are connected to external terminals attached to a side surface of the battery case (for example, see Patent Document 1). When a battery pack is formed by aligning multiple ones of the battery module, the external terminals each disposed on a side surface of the battery module are electrically connected to each other in series or in parallel, so that the battery pack having a predetermined voltage and capacity can be obtained.